Multiple use digital tone generator in telephone

Abstract

Electronic telephone set having DTMF tone dialling. By some slight additions to the logic circuits of the digital DTMF tone generator this tone generator is made suitable for generating a two-tone ringing signal, for supervising the frequency of the incoming ringing voltage and for generating a tone interval of approximately 0.1 s for the call-back function.

What is claimed is: 
     
       1. In an electronic telephone set having line terminals, number selection push-buttons, digital tone generator means having an oscillator having a fixed oscillator frequency and logic circuit means connected to said oscillator and comprising first frequency divider means for dividing said oscillator frequency by one of the plurality of divisors selectable under control of said number selection push buttons, a plurality of further control elements, and means for externally generating a control signal, the improvement comprising: detection means for detecting said externally generated control signal and generating a frequency control signal in response thereto;   additional frequency dividing means; and   means for interconnecting said additional frequency dividing means between said first frequency divider means and said selected one of said further control elements in response to said frequency control signal.   
     
     
       2. An electronic telephone set as set forth in claim 1, wherein said externally generated control signal is a line ring signal having an amplitude exceeding a predetermined threshold value; wherein said electronic telephone set further has an acoustic ringing signal generator, said acoustic ringing signal generator constituting said selected one of said further control element; and wherein said interconnecting means comprises means for connecting said additional frequency divider means to said acoustic ringing signal generator. 
     
     
       3. An electronic telephone set as set forth in claim 2, wherein said additional frequency dividing means comprises means for alternately dividing said oscillator frequency at a given rate by a first or a second additional divisor. 
     
     
       4. An electronic telephone set as set forth in claim 3, wherein said signal on said line terminals is an AC signal having a predetermined frequency; and wherein said given rate corresponds to said predetermined frequency. 
     
     
       5. An electronic telephone set as set forth in claim 2, wherein said interconnecting means comprises means for creating an upper and lower limit frequency signal in response to said frequency control signal; wherein said line ring signal has a predetermined frequency;   wherein said telephone set further has means for comparing said predetermined frequency to said upper and lower limit frequencies and generating a comparator output signal when said predetermined frequency is between said lower and upper limit frequencies; and   and wherein said interconnecting means couples said first frequency divider means to said acoustic ringing signal generator means under control of said comparison output signal.   
     
     
       6. An electronic telephone set as set forth in claim 5, wherein said electronic telephone set further has second frequency divider means having a second frequency divider input and a second frequency divider output, and third frequency divider means having a third frequency divider input connected to said second frequency divider output; wherein said interconnecting means further comprises a second switch for connecting said second frequency divider input to said first frequency divider means;   wherein said additional frequency dividing means comprises means for creating at least one additional division for said second frequency divider means thereby creating said upper limit frequency signal and a second divisor for said third frequency divider means, thereby establishing said lower limit frequency signal.   
     
     
       7. An electronic telephone set as set forth in claim 1, said set further having interrupter switch means for interrupting the subscriber line, and a line interrupter circuit for controlling said interrupt means, said line interrupter circuit constituting said selected one of said further control elements.